Compensating means for electrical borehole apparatus



DR zmihaazi I Dec. 3, 1946. c. B. AIKEN 2,411,843

COMPENSATING MEANS FOR ELECTRICAL BORE HOLE APPARATUS Filed Sept. 24,1942 2 Sheets-Sheet 1 5 47A; ILTERS 40a 30 [Yt'lf I PILOT OSCILLATOR[mime/14701? .?a I I cm: use/warm 4.9 AMPLIFIER 20- 47 5 F 46M ggN- v jZ f4 j 227 41 5.9 ,L 4 39d. 40a 'figfik -gs. 36 45 m I 405 M.kAMPLIF/ERS MENTOR CHARLES BIA/KEN 45" 0 45b *RECORDERS BY a M MM ATTRN EY$ i Dec. 3, 1946. c. BFAIKEN 2,411,843

COMPENSATING MEANS FOR ELECTRICAL BORE HOLE APPARATUS Filed Sept; 24,1942 2 Shet s-Sheet- 2 lO- CYCLE OSCILLATOR CYCLE OSCILLATOR INVENTORCHARLES B. Ami/v in). L

ll Va Patented Dec. 3, 1946 COMPENSATING MEANS FOR ELECTRICAL BOREHOLEAPPARATUS Charles B. Aiken, North Plainfield, N. J assignor toSchlumberger Well Surveying Corporation, Houston, Tex., a corporation ofDelaware Application September 24, 1942, Serial No. 459,508

6 Claims.

This invention relates to electrical bore hole apparatus and moreparticularly to means for compensating for the influence of externalconditions upon the operation of such apparatus.

It has become the generally accepted practice in petroleum engineeringto investigate different subjects of interest in a petroleum bore holefor the purpose of compiling data from which the levels of oil bearingformations and their approximate oil content may be deduced. Suchinvestigations are usually made electrically by lowering suitableelectrical apparatus into the bore hole and recording the responsesthereof at different depths by apparatus located either at the surfaceor in the bore hole. Frequently a plurality of difierent subjects ofinterest in the bore hole are investigated simultaneously.

Experience has shown that the operating characteristics of suchinvestigating apparatus may be influenced by conditions in the borehole. For example, the temperature in a bore hole increases with depth.Inasmuch as the electrical properties of the electrical components ofthe investigating apparatus may be a function of the temperature, theymay tend to change as the apparatus is moved through the bore hole,thereby producing undesirable modifications of its operatingcharacteristics.

It is an object of the invention, accordingly, to provide means forcompensating for unwanted variations in the operating characteristics ofelectrical bore hole investigating apparatus that may occur during a runin the bore hole.

Another object of the invention is to Provide compensating means of theabove character for compensating for undesirable variations in theoperating characteristics of electrical bore hole apparatus that areproduced by temperature variations in the bore hole.

A further object of the invention is to provide compensating means ofthe above character which is adapted to function automatically.

Still another object of the invention is to provide means for indicatingto an observer at the surface of the earth that an undesired variationin the operating characteristics of electrical investigating apparatusdisposed in a bore hole has taken place, and to provide manuallyoperable means for compensating for such variation.

The objects of the invention are attained by disposing with theinvestigating apparatus in the bore hole means for providing anelectrical signal that varies in substantially the same manner as theoperating characteristic of the investigating apparatus which is to becontrolled.

The response of the investigating apparatus,

' and the electrical signal, which will respond in substantially thesame manner to variations in a condition of the bore hole, such as itstemperature, for example, may both be visually indicated to an observerat the surface of the earth. The investigating apparatus is preferablyenergized from a source of electrical energy controllable from thesurface of the earth. Compensation for any undesired variations in theoperating characteristic of the investigating apparatus is provided byadjusting the electrical energy supplied by the source to maintain theelectrical signal substantially constant.

In another embodiment of the invention, the adjustment of the source ofelectrical energy to maintain the electrical signal substantiallyconstant is accomplished automatically in response to any deviation ofsaid signal from a reference value.

The invention may be better understood from the following detaileddescription of several representative embodiments taken in conjunctionwith the accompanying drawings, in which:

Fig. 1 is a schematic diagram of compensating means constructedaccording to the invention,

Fig. 2 illustrates schematically a modified form of the invention inwhich the compensation is accomplished automatically; and

Figure 3 illustrates a further embodiment of the invention.

While the compensating means of the present invention may be applied toa variety of electrical bore hole investigating apparatus, for purposesof illustration, it will be described in conjunction with an electricalwell logging system of the type described in the copending applicationof Hemi- Georges Doll; for Well logging system, filed J anuary 5, 1943,Serial Number 471,333. In such a system, indications are obtainedsimultaneously of the electrical resistivity of the surrounding earthformations at a plurality of diiTerent depths of investigation from thebore hole.

Referring now to Fig. 1, the electrical investigating apparatus II],which is adapted to be disposed in a borehole, comprises a plurality ofsimilar electrical oscillators Ila, b and lie, of conventional type,which are designed to generate alternating currents of 19, 47 and 80cycles, r spectively, for example. As indicated in the aforementionedcopending application of Henri- Georges Doll, any desired frequenciesmay be chosen, provided that none is a harmonic of the others, or of anypower frequency that may be present, such as cycles, for example.

The oscillators Ila, IIb and He may include one or more stages ofamplification, if desired.

The output terminals I2a and I3a of the oscillator Ila are connected bythe conductors Ma and I511, respectively, to the power electrodes A1 and3132, which are spaced apart a relatively large distance in the borehole. In similar fashion, the output terminal I2b of the oscillator Ilbis connected by a conductor I4b to a second power electrode A2, which isspaced apart a rela tively short distance from the electrode A1. Theoutput terminal I3b of the oscillator ND is connected by a conductorI51) and the conductor I50 to the electrode B1B2.

The oscillators I la, IIb and I I are adapted to be energized by adirect current source of electrical energy I6, located at the surface ofthe earth, one terminal of which is connected by a conductor I! to aground point I8 and the other terminal of which is connected through avariable resistance I9 to a conductor in the supporting cable (notshown). The lower end of the energizing conductor 20 is connected to oneinput terminal 2| of a conventional type low pass filter 22, which isdesigned so that its cut-off frequency lies below 19 cycles, the lowestfrequency generated by the oscillators Ila, IIb and II c. The low passfilter 22 serves to keep alternating currents of any frequencies out ofthe power circuits of the oscillators IIa, IIb and I I0.

The output terminal 23 of the low pass filter 22 is connected by aconductor 24 to the power input terminal 25a of the oscillator IIa, thepower input terminal 26a of which is connected by the conductors 21a and21 to a ground electrode AB disposed in the bore hole with the apparatusI0. In similar fashion, the power inputterminals of the oscillators IIband He are connected through similar conductors to the conductors 24 and21, corresponding parts being designated by corresponding referencecharacters with appropriate subscripts. The output terminal 28 of thelow pass filter 22 is connected to the input terminal 29 thereof and bythe conductors 30 and 2! to the ground electrode AB.

The filament circuits of the oscillators I la, I Ib and He, and of anyamplifier circuits that may be associated therewith, are preferablyconnected in series. To this end, the filament terminal 3Ia of theoscillator I la is connected by a conductor 32a to the ground conductor21 and the filament terminal 330 of the oscillator H0 is connectedthrough a voltage dropping resistance 34 and the conductor 35a to theenergizing conductor 20. The filament terminal 3Ic of the oscillator IIc is connected by the conductor 36 to the filament terminal 33b of theoscillator III), the filament terminal 3Ib of which is connected by theconductor 31 to the filament terminal 33a of the oscillator Ila.

As indicated in the above mentioned copending application ofHenri-Georges Doll, the 19 and 47 cycle alternating currents impressedupon the power electrodes A1 and B1B2 and A2 and B1132, respectively,create in the surrounding earth formations between those electrodes 19and 47 cycle alternating electric fields, respectively. Disposed apredetermined distance away from the power electrodes A1 and A2 is apick-up electrode M12, upon which are impressed potential differencesproduced by the created fields. These potential differences arefunctions of the electrical resistivities of the earth formations atlateral depths of investigation from the bore hole approximately equalto the spacings between electrodes A1 and M12 and A2 and M12,respectively.

The potential differences impressed upon the electrode M12 aretransmitted through a second conductor 38 in the supporting cable, theupper end of which is connected to the input terminals 39a and 39b ofconventional type band pass filters 40a and 401), which are designed topass 19 cycle and 47 cycle alternating electrical values, respectively.The input terminals Ma and 4Ib of the band pass filters 40a and 40b areconnected by a conductor 42 to the ground point I8 at the surface of theearth. The output terminals 43a and 43b of the band pass filter 4011 areconnected to a conventional type amplifier 44a, the output of which issupplied to a conventional type recorder 45a. In similar fashion, theoutput of the band pass filter 40b is amplified by a conventional typeamplifier 44b and supplied to a conventional type recorder 45b.

The output of the oscillator I I0, which is substantially constant inmagnitude, is also transmitted to suitable indicating apparatus at thesurface of the earth. To this end, the output terminal I2c thereof isconnected in series with a conductor I40 and a voltage dropping resistorMo to the conductor 38 in the supporting cable (not shown) and itsoutput terminal I3c is connected by the conductors I50 and 21 to theground electrode AB in the bore hole. At the surface of the earth, theoutput from the oscillator He is transmitted through the conductor 38 tothe input terminal 390 of a conventional type band pass filter 40c,responsive only to cycle alternating electrical values, the other inputterminal Me of which is connected by the conductor 42 to the groundpoint I8. The output of the filter 400 is amplified by a conventionaltype amplifier 44c and supplied to a conventional type recorder 450.

If the reading of the recorder 45c remains substantially constant as theinvestigating apparatus I0 is lowered through a bore hole, it is assumedthat the outputs of the oscillators Ila, IIb and He are constant andhave not changed. However, if a change is observed in the reading of therecorder 450, it is assumed that corresponding changes have taken placein the outputs of the oscillators Ila and III), perhaps because oftemperature variations in the bore hole. In order to compensate for thechanges thus produced, the observer, at the surface of the earth,adjusts the variable resistance I9 until the reading of the recorder45!: is restored to its original value. When that has been done, theoutputs of the oscillators Na and Nb likewise will have been restored totheir original values.

If desired, the compensation may be accomplished automatically, as shownin Fig. 2. In this embodiment of the invention, the output of the 80cycle amplifier 440 is transmitted to a controller 46, which is designedto provide a mechanical output that is directly proportional to theelectrical input thereto. Controllers of this type are well known in theart and need not be described in detail herein. The mechanical output ofthe controller 46 is made available at a shaft 41, on which is mounted aconventional type pinion 48 engaging a rack 49. Mounted on the rack 49is an insulated contact 50 which is adapted to slide along the variableresistance I9.

In operation, so long as the 80 cycle output of the oscillator Heremains constant, the slider 50 will remain fixed in position. However,as soon as any change occurs in the output of the oscil- .5 lator He,the contact 50 will be moved by the rack 49 and pinion 48 a sufiicientdistance in the proper direction to restore the output of the oscillatorllc to its original value. When that has been done, any similarvariation in the outputs of the oscillators i la and Ill) will have beencompensated for.

Instead of using an auxiliary or pilot oscillator llc to provide asignal that varies with the bore hole temperature in the same manner asthe outputs of the oscillators Ila and Nb, the output of one of thelatter oscillators may be employed as the source of the signal as shownin Figure 3. This may be accomplished by placing a resistance in serieswith the conductor [4b and impressing a potential related to the voltagedrop across the resistor 5| on conventional rectifying means 52.Inasmuch as the output of the oscillator Hb is impressed upon theelectrodes A2 and B132, the voltage drop across the resistor will,therefore, be proportional to the current flowing in this electrodecircuit which is a power circuit and not a measuring circuit. This powercircuit is completed through the bore hole fluid and the earthformations between the A and B electrodes. Normally, this bore holeresistance is very small, so that so far as the operation of therectifier circuit is concerned, the electrodes A2 and B1132 may beconsidered as shorted together or as having a, small relatively constantresistance between them. The rectifier 52 and filter 53 which areessentially connected in series, are then connected in parallel with theresistor 51 andthe formations between the electrodes A2, BiBz. If theelectrodes A2, B1Bz were shorted together, the potential across theresistor 5| would be the potential impressed upon the rectifier andfilter. In any event, the potential impressed upon the rectifier 52 andthe filter 53 is proportional to the current flowing in the circuit and,therefore, is proportional to the voltage drop across the resistor 5|.The output of the rectifying means 52 is filtered by a conventionalfilter 53 and the direct current component is transmitted through theconductors 54 and 38 to the surface of the earth. There, it passesthrough a filter 55, designed to pass only direct current, to aconventional recorder 56. If necessary or desirable, the direct currentmay be amplified before being supplied to the recorder 56.

It will be apparent that the direct current signal provided by theapparatus shown in Figure 3 may be employed to operate means forautomatically compensating for any undesired variations in substantiallythe same manner as shown in Figure 2.

It will be understood from the foregoing description that the inventionprovides new and improved means for compensating for undesired changesin an operating characteristic of electrical bore hole investigatingapparatus that may be produced by variations in a condition of the borehole, such as its temperature, for example. Moreover, by translating anyvariation in the control signal into a corresponding mechanical outputand utilizing that mechanical output to adjust the electrical energysupplied to the apparatus, the compensation may be accomplishedautomatically in response to any undesired variation in the output ofthe oscillators.

It will be further understood that the several embodiments describedabove may be modified in many respects within the scope of theinvention. The specific embodiments disclosed are intended merely to beillustrative and not restrictive. The

invention is not to be limited in any way thereby. but is susceptible ofnumerous changes in form and detail within the scope of the appendedclaims.

I claim:

1. An electrical bore hole investigating apparatus comprising electricalgenerating means adapted to be lowered into a bore hole and having anoutput that tends to Vary as a function of the temperature in a borehole, a source of electrical energy for energizing said generatingmeans, indicating means responsive to the response of said investigatingmeans, second generating means disposed in the bore hole with said firstgenerating means and energized from said source of electrical energy forproviding a signal at the surface that is distinguishable from theoutput of said first generating means and which varies as a function ofthe temperature in the bore hole in substantially the same manner as theoutput of said first generating means; and means for automaticallycontrolling the electrical energy supplied to said second generatingmeans to compensate for any deviation of the signal from the secondgenerating means from a reference value and for simultaneouslycontrolling the supply of electrical energy to said first generatingmeans to nullify the variations in its output due to temperaturevariations.

2. Electrical bore hole apparatus comprising investigating means adaptedto be lowered into a bore hole for exploring subterranean formations andhaving an output indicative of the formations traversed by said borehole, said investigating means being responsive to variations in thetemperature in the bore hol that cause undesirable variations in saidoutput, a source of electrical energy at the surface for energizing saidinvestigating means, indicating means responsive to the output of saidinvestigating means, a generating means disposed in the bore hole withsaid investigating means and energized from said source of electricalenergy for providing a signal at the surface of substantially constantmagnitude that is distinguishable from the output of said investigatingmeans and which varies in response to temperature in substantially thesame manner as the undesirable variations in the output of saidinvestigating means, and means for controlling in unison the electricalenergy supplied to said investigating means and said generating means toadjust said signal to said constant magnitude and simultaneouslynullifying the un desired variations in the output of said investigatingmeans.

3. An electrical bore hole apparatus comprising electrical generatingmeans adapted to be lowered into a bore hole and having an output thattends to vary as a function of the temperature in a bore hole, a sourceof electrical energy at the surface for energizing said generatingmeans, electrode means movable with said generating means and responsiveto the output of the latter for providing another output indicative ofthe earth formations traversed by the bore hole, an indicator responsiveto said another output connected to said electrode means, electricalsignalling means connected to said generating means for providing aremote signal that varies with th variations in the output of saidgenerating means due to temperature variations, and adjustable means forcontrolling the energy supplied to said generating means from the sourceto compensate for such variations in the output of said generating meansby adjusting said energy controlling means to restore said remote signalto a reference value.

4. An electrical bore hole apparatus comprising alternating electricalgenerating means adapted to be lowered into a bore hole and having anoutput that tends to vary as a function of the temperature in-a borehole, a source of electrical energy for energizing said generatingmeans, electrode means movable with said generating means and responsiveto the output of the latter for providing another output indicative ofthe earth formations traversed by the bore hole, an indicator connectedto said electrode means and responsive to said another output,electrical means connected to said generating means for producing analternating electric signal that varies with the variations in theoutput of said generating means due to temperature variations,electrical means for rectifying said electrical signal, indicating meanslocated at a remot point, an electric circuit connecting said rectifyingmeans and indicating means, and adjustable means for controlling theenergy supplied to said generating means from the source, to compensatefor such variations in the output of said generating means by adjustingsaid energy controlling means to restore said rectified value to areference value.

5. An electrical bore hole investigating means comprising alternatingelectrical generating means adapted to be lowered into a bore hole andhaving an output that tends to vary as a function of the temperature ina bore hole, a source of electrical energy for energizing saidgenerating means, electrode means movable with said generating means andresponsive to the output of the latter for providing another outputindicative of the earth formations traversed by the bore hole, anindicator responsive to said another output connected to said electrodemeans, an impedance connected in circuit with said generating means,electrical means for rectifying the voltage developed across saidimpedance, indicating means located at a remote point, an electriccircuit connecting said rec tifying means and indicating means, andadjustable means for controlling the energy supplied to said generatingmeans from the source to compensate for any variation in the output ofsaid generating means due to temperature variations by adjusting saidenergy controlling means to restor said rectified voltage to a referencevalue.

6. An electrical apparatus for use in investi-- gating subterraneanformations traversed by a bore hole where the output tends to varyundesirably and unpredictably as a function of its environment,comprising a first electrical apparatus whose output is to be maintainedconstant, a second similar electrical apparatus in close proximitythereto, an indicator at the surface of the earth connected to saidsecond apparatus, and means at the surface of the earth for altering theinput potential to said first and said second apparatus in unison toadjust said indicator to a reference value and maintain constant theoutput of said second apparatus.

CHARLES B. AIKEN.

